Vas Deferens (Ductus Deferens)
The vas (ductus) deferens is a muscular tube that is located within the spermatic cord and is a major component of the male reproductive system. It is a continuation of the epididymis and is involved in transporting spermatozoa from the epididymis to the ejaculatory ducts.
The vas (ductus) deferens may also be referred to as the ductus deferens. This article will talk about the anatomical course, histology, embryology and function of the vas (ductus) deferens, followed by any clinical pathology related to it.
The vas (ductus) deferens is 45 cm long and is initially convoluted but becomes straighter as it ascends in its course posterior to the testis and medial to the epididymis. When it reaches the superior aspect of the testis, it travels superiorly in the posterior aspect of the spermatic cord. The vas (ductus) deferens then crosses the inguinal canal before it emerges from the spermatic cord at the deep inguinal ring. It then curves around the inferior epigastric artery and ascends anterior to the external iliac artery. The vas (ductus) deferens then crosses the external iliac vessels in an oblique and slightly posterior direction.
Following this, it enters the lesser pelvis, where it is retroperitoneal, and traverses medially and posteriorly to the vesical vessels, obturator nerve and vessels, and the obliterated umbilical artery. The vas (ductus) deferens then crosses superior to the ureter at the posterolateral angle of the bladder. Once it crosses the ureter, the vas (ductus) deferens expands and is then referred to as the ampulla of the vas (ductus) deferens. It then passes between the upper aspect of the seminal vesicle and the posterior surface of the bladder in an anteromedial direction.
The vas (ductus) deferens then travels inferiorly along the base of the bladder, anterior to the rectum, before it joins with the duct of the seminal vesicle, at an acute angle, to form the ejaculatory duct.
The vas (ductus) deferens is usually supplied by a branch of the superior vesical artery but is occasionally supplied by a branch of the inferior vesical artery.
Venous & Lymphatic Drainage
Small veins from the vas (ductus) deferens usually drain into the testicular vein.
Afferent lymph vessels from the proximal portion of each ductus deferens generally ascends with lymph vessels of the testes to the lumbar lymph nodes. Lymph drained from the intermediate and terminal portion of the ductus deferens however, mostly drains into the external iliac lymph nodes.
The wall of the vas (ductus) deferens consists of three main layers. The outer layer is comprised of connective tissue whereas the middle layer is comprised of smooth muscle. An inner mucosal layer is also present.
The muscular layer of the vas (ductus) deferens consists of three layers:
- an inner longitudinal layer
- a thick intermediate circular layer
- an outer longitudinal layer
These layers are innervated by the sympathetic nervous system.
The vas (ductus) deferens consists of an inner epithelial lining with supportive lamina propria. The epithelium lining the vas (ductus) deferens is pseudostratified columnar epithelium and is very similar to the epithelium seen in the epididymis. This inner layer is comprised of longitudinal folds, which allows the vas (ductus) deferens to expand during ejaculation.
The vas (ductus) deferens develops from the mesonephric or Wolffian ducts. These ducts are derived from the mesoderm, the middle layer of one of the three primary germ layers in the embryo. The other two layers are the ectoderm and the endoderm. Various male reproductive structures are formed from budding off the mesonephric ducts like the seminal vesicles and the epididymis. After the budding of these structures, the remaining mesonephric ducts develop a muscular coat and form the vas (ductus) deferens.
The vas (ductus) deferens is involved in transporting spermatozoa from the epididymis to the ejaculatory ducts. During ejaculation, the sympathetic nervous system innervates the muscular layers of the vas (ductus) deferens and causes them to produce strong peristaltic contractions in order to aid in the propulsion of the spermatozoa.
The vas (ductus) deferens can be easily palpated between the testes and the superficial inguinal ring because it has a thick smooth muscle wall. A useful method of male sterilisation or contraception is a vasectomy. The procedure involves an incision in the superior aspect of the scrotum and ligation or excision of the vas (ductus) deferens. This prevents transportation of the spermatozoa to the ejaculatory duct and results in the absence of spermatozoa in the ejaculate. The spermatozoa then degenerate in the epididymis and proximal portion of the vas (ductus) deferens.
Reversal of a vasectomy is usually successful if the patient is less than 30 years of age and also underwent the vasectomy operation less than 7 years ago. Reversal occurs by reattaching the ends of the ligated or excised ductus deferens, with the aid of an operating microscope.
Congenital absence of the vas (ductus) deferens is referred to as vasal aplasia. This results in azoospermia, the absence of sperm in the semen. However, spermatogenesis, the production of sperm, is usually normal. Therefore, pregnancy can still be achieved using assisted reproductive technology. Vasal aplasia can occur in men with cystic fibrosis, so men with vasal aplasia should be screened for the presence of this disease.
Infection of the genitourinary tract by the bacteria Mycobacterium tuberculosis can result in genitourinary tuberculosis. Genitourinary tuberculosis can cause obstruction of the vas (ductus) deferens by deposition of granulomas or by causing scarring. This can also result in azoospermia and infertility.